1. Field of the Invention
The present invention relates to a jig for holding and conveyance and a holding and conveyance method suitable for a process in which electronic components and the like are mounted on the surface of a printed circuit board in the form of a thin plate such as a flexible printed circuit board, or a process in which the printed circuit board is manufactured.
2. Description of the Related Art
In every kind of electronic appliance from mass-produced appliances such as television sets to appliances for use in rockets or the like of which high reliability is required, printed circuit boards are being presently used for the purpose of improving productivity, ensuring mass production quality, improving reliability, etc. Ordinarily, printed circuit boards are constructed so as to have a conductor pattern on an insulated substrate surface. In recent years, however, flexible printed circuits (hereinafter referred to as “FPC”) having a conductor pattern on a surface of a film-like insulated substrate have been provided to meet demands for reducing the size and weight of electronic appliances. For FPCs, a method of mounting electronic components on the conductor pattern surface, i.e., the surface mount method, is being widely used.
The surface mounting method is ordinarily carried out as described below.
A plurality of FPCs are first placed on a surface of a jig for holding and conveyance in the form of a plate, and a heat resistant adhesive tape is adhered to peripheral portions of the FPCs to support the FPCs. Thereafter, cream solder is applied to conductor pattern surfaces on the surfaces of the held FPCs according to the positions at which electronic components are mounted, etc. After mounting the electronic components on the cream solder applied portions, these portions are heated to melt the cream solder, and the molten cream solder is set, thereby connecting the electronic components to the FPCs. Thereafter, the adhesive tape is peeled off the jig, and the FPCs are removed.
In the use of the above-described conventional jig for holding and conveyance, there is a problem in that since there is a need to first peel off the adhesive tape when the FPC is removed from the jig, the number of manufacturing steps is increased. There is also a problem in terms of cost since the adhesive tape is lower in durability and in heat resistance and needs replacement after being used about one time.
As a solution of this problem, a method has been proposed in which a weak-adherence adhesive layer, e.g., a silicone resin layer, is formed on the entire surface of the above-described jig, and FPCs are held by being placed on the surface of the silicone resin layer (e.g., Japanese Unexamined Patent Application, First Publication No. Sho 63-204696). In this case, the heat resistance and the separability of the FPCs from the jig surface are good and realization of low-cost high-efficiency production can therefore be expected. In this case, since the silicone resin layer is uniformly formed on the jig surface, there is a manufacturing problem in that when a metal mask used for application of cream solder to the surfaces of FPCs held on the resin layer surface is separated from the FPC surfaces after application of the cream solder, the metal mask is adhered to portions of the resin layer (between the adjacent FPCs) where the FPCs are not placed, and cannot be suitably separated therefrom.
There is also a problem in that part of the silicone resin layer is dissolved during the cream solder application step or the like, and the dissolved part is transferred onto the FPC surfaces and attached to conductive portions formed on the FPC surfaces to cause failure in connecting electronic components.
In particular, since low-molecular-weight siloxane, which is not formed into a polymer by polymerization, ordinarily remains in the silicone resin, the silicone resin has a characteristic such that the remaining low-molecular-weight siloxane is exposed in the silicone resin layer surface when the silicone resin is heated. Therefore, there is a problem in that, as in the above-described jig arrangement, when a silicone resin layer is uniformly formed on a plate surface and is heated as described above while the entirety of an FPC is placed and held on the silicon resin layer surface, low-molecular-weight siloxane is exposed in the silicone resin layer surface and the exposed part is transferred onto the conductor pattern on the FPC surface. In this case, an electronic component or the like cannot be suitably connected to the portion of the conductor pattern at which the above-described transfer has occurred, and there is a possibility of the occurrence of a connection failure.